When water is to be pumped out of an outdoor pit, reservoir, or canal, it is important to prevent debris, such as leaves, sticks, discarded plastic and paper articles, stones, etc., from entering the pump. Rotary self-cleaning strainers that contain cylindrical screens for performing the straining function are often used for this purpose.
The strainer is attached to the end of a conduit and placed in the body of water that is to be pumped. The pump is operated to suck water through the strainer and conduit, as the strainer screen prevents debris from being sucked into the conduit along with the water. Certain debris may adhere to the screen's exterior due to the pump suction force. However, the continued adherence of such debris to the screen's exterior, and resulting impairment of flow through the screen, is prevented by rotating the screen past a nozzle structure which is disposed on the interior of the screen and directs water outwardly through the screen to dislodge the debris. The water is fed under pressure to the strainer through a separate supply line which may be tapped into the pump's outlet. The water acts on only a limited circumferential zone of the screen at any given time to force adhering debris away from the exterior of the screen as the screen revolves past the nozzle structure. The remainder of the screen serves to pass the flow of water that is being sucked by the pump.
Commonly assigned U.S. Pat. Nos. 4,822,486 and 5,108,592 disclose new and improved rotary self-cleaning strainers of this general type. The patented strainers possess a number of novel and unique features which individually and collectively relate to the patented improvements. One feature relates to the use of the nozzles to simultaneously both rotate and clean the screen. In order to do this each nozzle is aimed such that it emits pressurized water that has both a tangential and a radial component of velocity at its reaction point on the screen. The screen is a perforated aluminum sheet that encloses the circumference of a spool-like frame.
Continuing efforts by the assignee have resulted in further improvements in rotary self-cleaning strainers, and they are the subject of the present patent application. One improvement relates to the use of a multi-apertured cylindrical plastic pipe in the rotary portion of the strainer. One purpose of this pipe is to provide support for the strainer screen which is wrapped around the circumference of the pipe. Another is to provide reaction surfaces against which drive nozzles emit pressurized water to rotate the rotary portion of the strainer.
The reaction surfaces are provided by a circumferentially extending succession of relatively small apertures, or holes, that extend through the sidewall of the pipe. One or more drive nozzles at a particular circumferential location, or locations, is, or are, aimed at this succession of apertures to direct pressurized water toward the succession of apertures with velocity that acts predominantly tangentially of the strainer axis at reaction points with the apertures. The pressurized water acts on portions of the surface area of each aperture that more or less face the drive nozzle(s). The apertures are spaced sufficiently close together that circumferential motion that is imparted to the pipe by virtue of the drive nozzle(s) acting on a particular one or ones of the apertures produces a sufficient amount of circumferential motion that an immediately succeeding aperture or apertures comes under the influence of the drive nozzle(s) whereby continuing rotation is imparted to the rotary portion of the strainer.
Other larger apertures, or holes, in the sidewall of the pipe provide for the water being pumped to pass into the interior of the pipe while the overlying strainer screen strains debris from it. Since the suction force developed by the pump is typically large enough that the debris may tend to adhere to the outside of the screen, the strainer also includes one or more cleaning nozzles aimed at these other larger apertures to dislodge such adhering debris. Because the rotary drive force is being efficiently imparted by the drive nozzle(s) acting on the smaller apertures, the cleaning nozzle(s) may be aimed substantially radially outwardly as viewed along the axis of the strainer to take advantage of maximum debris-dislodging force. Thus the cleaning nozzle(s) is (are collectively) incapable of imparting rotation to the rotary portion of the strainer.
In one embodiment of strainer, the drive nozzle(s) is (are) arranged to produce only uni-directional rotation of the rotary portion of the strainer. In another embodiment, drive nozzles are arranged to produce bi-directional rotation, meaning that the rotary portion can be rotated in one direction and then reversed. Such a reversing feature may be desirable for certain strainer constructions and/or strainer applications.
The strainer that will be illustrated in the accompanying drawings is designed for only partial submersion in a body of water, as distinguished from complete immersion. Broader principles of the invention are however also applicable to strainers that are intended to be completely submerged in water.
A further feature that guards against excessive suction that might otherwise detrimentally collapse the strainer screen into the apertures in the pipe's sidewall is in the nature of a vacuum relief valve.
One of the advantages of the invention is that the strainer screen can be a woven stainless steel wire mesh screen. The ability to use this medium for the strainer provides potential cost economies and service advantages. To provide for convenient assembly and disassembly of the strainer screen to and from the pipe, wherever and whenever needed, the woven wire mesh is backed with a sheet of plastic backing that affords some rigidity, yet can be wrapped along with the woven wire mesh around the outside of the pipe. The plastic backing sheet is apertured in the same pattern as the apertures in the sidewall of the pipe so that when wrapped around the pipe, the apertures in the two parts are in registry. The woven wire mesh and the backing sheet are held together by means of U-shaped channel that is fitted over the common perimeter margin of the two when they are placed together with their apertures in registry. This then forms an assembly that is secured to the pipe by means of screws that pass through the assembly at various locations around its perimeter margin just inwardly of the channel to thread into the sidewall of the pipe. The channel provides a seal of the perimeter margin of the assembly to the pipe when the assembly is completely fastened to the outside of the pipe.
Annular end closure discs close the opposite axial ends of the multi-apertured pipe to the non-rotating central core of the strainer which comprises a suction pipe and a supply pipe. These end closure discs are rigid plastic, and when their perimeters are fastened to the axial ends of the multi-apertured pipe, a strong structural foundation for the rotary portion of the strainer results. These annular end closure discs include means providing for the journaling of the rotary portion of the strainer on the central core about the strainer's longitudinal axis. Because of the use of the cylindrical plastic multi-apertured pipe as part of the combination with these end closure discs, there is no need for any additional structure to extend longitudinally between the annular discs. This has the advantage of eliminating the tie rod structures that are present in the strainers of the aforementioned commonly assigned patents to join the annular end closure discs. The construction of the present invention also offers the advantage of being able to replace screen without having to disassemble any of the underlying screen support structure.
The foregoing features and advantages of the invention, along with additional ones, will be seen in the ensuing description and claims which are accompanied by drawings. The drawings disclose a presently preferred embodiment of the invention according to the best mode contemplated at this time for carrying out the invention.